The present invention relates to a display device applicable to a copier for displaying a copying area.
It is a common practice with a copier to dispose a scanner below a glass platen. While the scanner scans the underside of a document laid on the glass platen, the resulting reflection from the document is incident on the surface of a photoconductive element or on an image sensor. A scale is located at each of two or four sides of the glass platen which the operator of the copier may reference in the event of positioning a document on the glass platen.
The maximum document size available with many of copiers for office use, for example, is A3. This kind of copier has a glass platen dimensioned slightly greater than A3 size. However, since documents of A3 size are rarely copied, compared to documents of the other sizes, only part of the glass platen is usually used as an area for reading a document image, i.e., an effective image reading area. Specifically, to copy a document of A4 size or similar size smaller than the glass platen, the operator has to set the document at a particular area matching the effective image reading area on the glass platen by hand. The above-mentioned scales help the operator so position the document on the glass platen. Specifically, the scales are each provided with graduations representative of regular sizes available with the copier, e.g., A3, B4, A4, B5 and A5. To reproduce a document of A4 size, for example, the operator has only to position the document at the graduation A4 of the scales.
In practice, however, positioning a document by referencing the scales is not easy. Particularly, assume a center registration type copier in which the effective image reading area is determined on the basis of the position of an axis passing the center of the short sides of the glass platen in parallel to the long sides. Then, even when a scale is arranged around all of the four sides of the glass platen, the actual effective image reading area adjoins only one scale and is spaced apart from the other three scales. Therefore, to position a document smaller in size than the glass platen at the effective image reading area, the operator has to determine the approximate position of the effective image reading area with the eye by looking at the three scales slightly spaced apart from the area for positioning the document and the single scale adjoining the area. This kind of scheme prevents the document from being accurately positioned and, in addition, forces the operator to take greatest care in positioning the document.
Moreover, when the operator adjusts a magnification to a desired value by using, for example, a zooming function, the effective image reading area differs from regular sizes. Hence, even with a corner registration type copier having a vertical and a horizontal scale contacting two adjoining sides of an effective image reading area, it is impossible for the operator to read the accurate position of the rectangle of the area on the scales. Therefore, the positioning operation on the glass platen is extremely difficult and time- and labor-consuming.